1. You can use the EMS administration utility, login to the EMS server and
use show messages command on the EMS queue.
2. You can write a rulebase for monitoring and alerting when there is a
pending messages in EMS queues.

If you know /queue name you can see in EMS server using this command ----show queue queue name-----but in Gems it is very easy all queues at the same time with all properties.you can view pending messages and intotalmessages,senders and receivers etc...
Thanks,